Surface-applied poultry litter generated using a phytase-amended diet may release less phosphorus (P) to runoff water than does litter from a conventional diet. The release of soluble reactive (SRP) and total dissolved P (TDP) from litter generated under conventional and phytase-amended diets was examined in three studies: 1) batch desorption, 2) flow-through cell, and 3) field micro-plot. In Study 1, samples of litter (10 from conventional, C, and 20 from phytase-amended, A, diets) were extracted with water at litter: water ratios from 1:5 to 1:200. Phosphorus in A litter was significantly less at the 1:10 extraction ratio; however, there was no difference at wider ratios. When desorbed P was plotted against solution concentration, all isotherms were sigmoidal. In Study 2, water was passed uniformly through samples of litter (~ 4 g in 4 cm diameter by 1 cm deep cell) at a flux of 7.5 cm h-1 for 1.5 h and litter effluent collected in fractions for analysis. Less P was lost from the A than from the C litter, however, less P was recovered than in Study 1. Study 3 compared losses of P from litters A and C in field runoff from 324 cm2 plots during a series of simulated rainfalls (7.5 cm h-1 for 1 h each). Although significantly less P was initially lost from the A litter, P losses from the A and C litters tended to converge over the course of Study 3. Thus, whereas there was less TDP in the A than in the C litter, differences in SRP and TDP are small.